The present invention is a stile extender for use with a ladder to enable the effective length of one or both of the stiles of the ladder to be extended and thereby to enable the ladder to be used more safely upon a surface which is inclined in a direction parallel to the plane of the ladder.
The stability of a ladder which is leaned against a wall, for example, may be seriously jeopardised if the ground surface supporting the ladder slopes in a direction parallel to the wall. With that problem in mind, it was suggested in UK Patent Specification No 1578143, which was published in 1980, that the effective length of a ladder stile might be increased by securing to it a device described therein. That device took the form of a housing rigidly attached to the ladder stile, a second element slidable longitudinally within that housing, a longitudinal slot in the housing and a locating member which was a feature of the second element and ran in the slot; the slot had transverse recesses into which the locating member could fit to prevent linear movement of the second element within the housing.
While the device described in the above-mentioned patent specification would appear to be potentially suitable for the purpose described, it exhibits two disadvantages in practice. First of all, the transverse recesses by their very nature must be spaced apart by sufficient intervals to give integrity to the structure of the housing, which of course must bear the weight of the support ladder and its user. Thus the adjustment of the length of the ladder stile is essentially a step-wise adjustment with no capacity for close setting of the stile length. Secondly, the necessary design of the device inevitably makes the product relatively expensive to produce and may as a result discourage a potential user from purchasing what could otherwise be an advantageous aid to ladder safety.
An alternative form of what is identified as a xe2x80x9cladder levelling devicexe2x80x9d is described in International Specification No WO 99/25947, which was published some eighteen years after the above-mentioned UK specification. The device described in that international specification is of a much more complicated design than the earlier device. Although it is suggested in Specification No WO 99/25947 that the device described therein may be either mounted within a ladder stile or attached to the side of a ladder, in fact the only specific device described is one for fitting within a stile. That device is shown to be a close fit within a ladder stile, to the extent that each different ladder stile dimension would require a different size of the stile extender. The device there described and illustrated has a large number of parts and is of such apparent length that, if fitted as illustrated within the stile of any conventional ladder, it would appear to require the lowermost ladder tread to be located unduly and inconveniently high above ground level. The complexity of the design is well illustrated by FIGS. 1 and 2 and in particular by the cross-sectional views 1xe2x80x941 to 9xe2x80x949 inclusive.
Because a ladder stile extender is in most situations an optional fitting of which the prime function is to enhance ladder safety in certain specific conditions, the adoption of such a device has been in general slow in practice. What the potential user appears to require is a relatively simple device which is consequently relatively cheap to purchase and install. Of course the device must nonetheless be very reliable in use and should reduce or avoid the foregoing disadvantageous features of the above-described prior proposed devices. It is an object of the present invention to provide such a device.
The ladder stile extender according to the present invention comprises two elongated members one of which is slidable within the other and having means for securing one of said members to a ladder stile and the other of the said members functioning as a stile extender or having means to secure it to a stile extension, a set of generally parallel irregularities associated with each of said members for interengagement with those on the other member, means for moving the two sets of irregularities into and out of engagement with each other, and locking means to secure said members together with said sets of irregularities so engaged. It is particularly preferred that the two sets of irregularities be each a set of generally parallel teeth, in particular such teeth extending transverse to the direction of relative movement of the two members.
It is a very important advantage of the ladder stile extender according to the present invention that it is adapted for production in a very simple and relatively inexpensive form, for use internally but more preferably externally upon ladder stiles of a wide range of cross-sectional dimensions, with a high degree of security against ladder collapse, which combination of features is not shown by any of such stile extenders as may be currently available and in use. Moreover, the design of the present novel stile extender enables the relative linear movement of the two interengaging members to be rendered continuous or nearly so, thereby enabling the extending of the relevant stile to be more readily matched to that required than has hitherto been possible.
In general it is preferred that the outer elongated member be secured to the ladder stile and that the inner such member be the one which, in the extended condition of the ladder stile extender, engages the ground either directly or via an appropriate foot or via a ground-engaging ladder base support. As indicated, the stile extender may be fitted within a ladder stile if desired. However if that is the desired arrangement then it is necessary for the extender to be of such a dimension as will allow it to fit within the ladder stilexe2x80x94and indeed it may even then be necessary for the extender to be of different external dimensions for each ladder size. It is a particularly preferred feature and specific advantage of the stile extender according to the present invention that it may be secured to the external surface of the ladder stile. If secured to the external surface in this way, the stile extender may be secured either to the outwardly-facing surface of the stile or to that stile surface which faces the other stile of the ladder. The design of the stile extender is such that it may be of such a size as will fit below the lowermost rung of the ladder with that rung at the conventional level, for example of the order of 6 or 7 inches (15.24 to 17.78 cm) above the ground.
The two mutually slidable members are particularly preferably of rectangular, including square, cross-section. The attachment of one of said members to the ladder stile may readily be achieved by means of bolts, preferably two said bolts, extendable from the adjacent face of the member through corresponding bores in the ladder stile. Other forms of attachment may be adopted, in particular when it is desired or necessary to avoid penetrating the stile.
The second member is preferably of a matching cross-sectional shape to that of the hollow interior of the first member and is particularly preferably a close sliding fit within that first member. Thus it is particularly preferred that it also be of rectangular, including square, cross-section. The linear dimensions of the two members are a matter of design choice but the maximum extent of their linear relative movement determines the amount by which the ladder stile may be extended.
The two sets of generally parallel irregularities, which for the sake of convenience will be hereinafter referred to as teeth, may cover a similar area in each case but that is not necessary. Preferably, one set of teeth extends, in the direction of relative movement of the relatively slidable members for a shorter distance than the other set, that is there are fewer such teeth. The fewer teeth are preferably, but not necessarily, those associated with the movable said member. The teeth themselves may if desired each be inclined towards the teeth on the other member in a direction to give enhanced resistance to undesired relative movement of the two members. The total area of interengagement of the two sets of teeth may be selected to reflect the nature of the duties for which the ladder itself is likely to be adopted but it is preferred that that area be at least 6 sq. cms. The teeth may, if desired, be formed by pressing but it is particularly preferred that they be formed by cutting into an initially planar surface or by extrusion.
When the length by which the relevant ladder stile is extended is to be adjusted, the two sets of teeth are brought out of and into engagement with each other. To this end, one of the two members must be moved away from and towards the other member, thereby allowing linear relative movement of the two members. By way of example, the two members may be interconnected by means of threaded bolts, enabling the teeth to move linearly apart. However, in a preferred form of the invention, the two sets of teeth are brought into and out of engagement with each other by relative pivoting of the two sets. The set of teeth which actually pivots is much preferably that set of fewer teeth which, as indicated above, is preferably that on the movable member. It is particularly preferred that the two sets of teeth be urged together by spring means, in particular a strong said spring, in the absence of any pressure applied, for example by the user, to urge them apart, thereby allowing the user""s hands to be free to level the ladder. Thus in a particularly preferred form of the ladder stile extender according to the present invention, a relatively shorter movable member carrying a relatively smaller number of transverse teeth is pivoted relative to the longer member having a larger number of such teeth and is urged into a position wherein the two sets of teeth are interengaged by means of a spring.
When the two sets of teeth are interengaged, the two relatively movable elongated members are duly secured together by means of the locking means. That locking means may take any desired form but in one preferred form it is a threaded bolt or a nut or wing-nut threaded upon a threaded bolt; in another particularly preferred form, the two relatively movable members are secured together or released, in a very convenient manner, by means of a cam-lock.
Thus, in one preferred form of the stile extender according to the present invention, the first elongated member is secured to the ladder stile and has a number of transverse teeth across its length. The second elongated member is slidable within the first such member and carries a smaller number of such transverse teeth associated with it upon a component pivoted upon the second elongated member so as to permit the two sets of teeth to engage and disengage. The two sets of teeth are urged into mutual engagement by a spring and retained in their mutually engaged position by means of a threaded bolt and/or nut or by means of a cam-lock.
The device according to the present invention thus enables one of the elongated members to be moved into direct or indirect engagement with the adjacent ground surface and to be retained securely and safely in that position. In this way the ladder stile is effectively extended into engagement with the ground. If desired, two such stile extenders may be used, one attached to each of the stiles of the ladder. The stile extender or extenders is preferably so designed, and preferably so mounted upon the associated ladder stile, that it may be retracted beyond the lower edge of the stile when not required to be used.
Preferably the lower end of the slidable elongated member is specifically adapted for stable engagement with the adjacent ground surface or with a ladder base stabiliser of the type designed to prevent slippage of the ladder in a direction away from a wall. For example, the elongated member which extends downwardly may advantageously carry a ground-engaging foot, which preferably is pivoted upon the lower end of that member. The foot may advantageously be part-spherical, for example, hemispherical, in shape, with a generally flat ground-engaging lower surface, preferably of enhanced frictional characteristics, able, by virtue of its mounting, to lie flush with the ground surface whatever the inclination of the ladder stile.
While the ladder stile extender according to the present invention may be used alone to adapt a ladder foot to an inclination of the ground in a direction parallel to the plane of a ladder, the extender may particularly advantageously be used with a ladder brace devised to stabilise a ladder foot against slippage in a direction away from a wall against which the ladder is inclined. For example the stile extender may be used in combination with a ladder stabiliser such as is the subject of my UK Patent No. 2216168. As one possibility, one or two stile extenders may be attachable, preferably removably, to the ladder stabiliser. Most advantageously, the stile extender of the present invention may be used as a feature of the stabiliser which is the subject of my co-pending UK Patent Application No. 0008830.2. In that application, I have described a ladder stabiliser which comprises a rigid, generally flat base having a linear channel extending along a first, upper surface thereof, which channel is defined by a pair of generally parallel, upwardly extending channel side members having upper edges directed towards each other, and at least one ladder attachment by means of which a ladder stile may be extended downwardly. The ladder attachments may, for example, be two of the stile extenders according to the present invention.
When the stile extender of the present invention is used in combination with a rigid, generally flat base as described, the lower end of the downwardly-extending elongated member may carry a foot which is specifically shaped to match the cross-section of the linear channel formed on the base. For example, the channel may have an essentially circular cross-section and the stile extender foot may itself have such a circular cross-section; for example it may be spherical.